The present disclosure relates in general to optical sensing and more particularly to the use of reflective optical sensors. Reflective optical sensors are often used in input devices with closed surfaces without any mechanical components (i.e. buttons). Their purpose is to sense a movement in the proximity of the surface or a touch upon it and their range of sensitivity is generally limited. The inventive method and apparatus disclosed herein significantly extends the effective range of a reflective optical sensor making the sensing process almost independent from the shape and thickness of an input device's front surface, which allows greater flexibility in the mechanical design of the input device.
FIG. 1 illustrates a prior art reflective optical switch. A reflective optical sensor 1 contains an infra-red (IR) emitter 2 and a complementary IR receiver 3. The reflective optical sensor is positioned at a distance of 1 cm from a transparent active surface 4 which represents the maximum effective range of the reflective optic sensor. The effective range can be greater or lesser depending on the power and sensitivity of the IR emitter and receiver respectively, but in general for effective operation reflective optical sensors must be placed in close proximity to a transparent surface to facilitate the reflection and reception of emitted IR off of an approaching triggering object. A triggering object 5 is shown adjacent to the transparent surface at an active region, or at a position that leads to a successful reflection of IR light emitted by emitter 2 off of object 5 and back towards IR receiver 3. A successful reception of IR light by the receiver 3 generates an electrical signal which can be used to effect a change in the operation or status of an electronic device (not shown) connected to the reflective optical sensor. Triggering object 5 can be any manner of object having a surface which will reflect IR light but is typically a person's finger which has led to the description of such a reflective optical switch as “touch sensitive”.
Reflective optical sensors used to sense movement in the proximity of the surface or to detect a touch of the surface near the sensor contain advantages over mechanical systems such as buttons. Mechanical systems are more prone to wear and tear because of their movement, and sensors can be used in connection with graphical user displays to promote flexibility in display design.
The physics of optical sensors, however, limits the range of the effective distance of the movement to the sensor. In general applications, the sensor must be most proximate to the surface in order for the sensor to detect a reflection. Accordingly, the design of such sensor systems is somewhat limited with respect to the positioning of the sensors and the thickness and shape of the touch surface. Accordingly, there is a need for a system of reflective optical sensors to break free of space and positioning constraints to permit innovative designs of touch sensor pads.